POS0056 LYME ARTHRITIS. A RARE BUT IMPORTANT CAUSE OF MONO – OR OLIGO ARTHRITIS IN DENMARK: A CASE SERIES OF LYME ARTHRITIS IN FOUR DANISH MALE PATIENTS
Authors: A. Ünlü, N. S. Andersen, S. Skarphedinsson, S. L. Larsen, S. Chrysidis, P. Lage-Hansen
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Lyme arthritis (LA) is a rare manifestation of Lyme borreliosis in Denmark with an unknown incidence [1-2]. Typically, LA present with persistent or intermittent mono-arthritis in large joints especially the knees [3-4]. Clinically, LA does not differ significantly from other rheumatological oligoarthritic disorders, and due to a supposed low incidence, it poses a differential diagnostic challenge with risk of misdiagnosis. <h3>Objectives</h3> To describe a case series of four Danish patients diagnosed with LA from 2021-2022. <h3>Methods</h3> A case series. <h3>Results</h3> We describe a case series consisting of four Danish patients diagnosed with LA at the Department of Rheumatology, Esbjerg Hospital within a year (2021-2022). All patients presented with recurrent knee joint swelling, yet one patient also had arthritis in the upper extremities. All four patients reported previous tick bite, but none had a history of erythema migrans. The diagnosis was delayed up to one year due to lack of attention to LA as a potential differential diagnosis. The diagnosis was established based on the Borrelia burgdorferi sensu lato complex (B.b.s.l.) anti-IgG antibodies in patient serum and detection of B.b.s.l. DNA by real-time PCR of synovial fluid. All patients received antibiotics in a four-weeks period. However, one patient was re-treated because of recurrence of joint swelling in the upper extremities and detection of B.b.s.l. DNA by PCR in synovial fluid from the wrist joint, after completing the first line-antibiotic regimen. Three patients have fully recovered and have shown no sign of arthritis in a period ranging from 4 to 15 months. One patient is currently treated with Methotrexate. <h3>Conclusion</h3> This case series demonstrates that LA is an important differential diagnosis in persistent or intermittent mono – or oligo arthritis, especially in the knee joint. Lack of routine assessment of tick risk behavior, antibody status and/or assessment of the presence of B.b.s.l. DNA in synovial fluid by PCR methods, can lead to underdiagnosed cases. Obviously, insufficient examination can lead to a falsely assumed low incidence. It could be considered that the low incidence of LA in Denmark partly is caused by lack of attention to B.b.s.l. as a possible explanation for mono- or oligo arthritis. Clearly, this can lead to mistreatment. <h3>References</h3> [1]Müller T et. al. Lyme arthritis is rare in Eastern Denmark. Dan Med J. 26. oktober 2021;68(11):A05210423. [2]Dessau RB et. al. Utilization of serology for the diagnosis of suspected Lyme borreliosis in Denmark: survey of patients seen in general practice. BMC Infect Dis. 1. november 2010;10:317. [3]Berglund J et.al. Lyme arthritis--a common manifestation in a highly endemic area in Sweden. J Rheumatol. april 1995;22(4):695–701. [4]Corre C et. al. Lyme arthritis in Western Europe: a multicentre retrospective study. Eur J Clin Microbiol Infect Dis. januar 2022;41(1):21–7 <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.